Accommodation is the ability of the eye to create a sharp image on the retina of an object located at any given distance. Thereto, the required adjustment of the refractive power occurs essentially through the elastic deformation of the lens. The possible maximum change in refractive power is called amplitude of accommodation. It can amount to 16 dioptors and decreases with age.
Presbyopia or age-related farsightedness, i.e., the reduced amplitude of accommodation of the eye lens, is the result of an age-related hardening and/or thickening of the eye lens. Typically, an eye lens is called presbyopic when its amplitude of accommodation drops below 3 dioptors. Presbyopia is not a pathological process but a natural consequence of old age, starting at age 40.
In ophthalmology it has been suggested to restore improved deformability of a hardened lens through suitable incisions or creation of bubbles by means of a refractive surgical therapy, particularly photodisruption or other incisions. Thereby, the accommodative capacity of the lens is to be partially regenerated.
Ophthalmological laser systems for presbyopia therapy have already been described in prior art. For example, WO 2008/017428 A2 discloses a navigation device for optical analysis and treatment of the inner structure of the eye lens.
The navigation device is equipped with a detection device and a treatment device, whereby the detection device can comprise a confocal detector and/or a confocal laser scanner. A photomultiplier (PMT) or an avalanche photodiode (APD) is suggested as detector. The same laser is provided for the analysis of the inner structure as well as treatment, whereby the detection beam path is coupled by means of a beam splitter into the treatment beam path. Thereby, the laser light, backscattered in the eye lens, is for analysis, in order to determine position, geometry, and structure of the eye lens. By means of the detected inner structure and the individual geometric form of the eye lens, the cut geometries to be produced during treatment are determined. For said purpose, a basic pattern is adjusted to the detected individual geometry.
A problem is that the intensity of the light backscattered in the eye lens is very low due to the inherent properties of the eye lens—for a high imaging quality, the scatter must be as slight as possible. As a result, the detection contains a relatively great number of flaws.